This invention relates to a bend segment for a chain conveyor comprising a conveyor chain movable over a track including at least one bend zone, the bend segment consisting of at least one substantially U-shaped plastics element and the legs of the U-shaped element forming the rails over which the chain can move, while the chain comprises links each comprising a substantially rectangular bearing surface and a connection system located below the bearing surface, the successive links being pivotally coupled to each other through the connection systems thereof and consisting at least partly of a magnetizable material, and permanent magnets are arranged at least in the connecting portion between the legs of the U-shaped element.
Such a bend segment for a chain conveyor is disclosed in European patent application EP-A-0.286.173. This bend segment is suitable for a chain conveyor over which runs a chain whose links are substantially made of plastics, while the permanent magnets exert a downward force on the hinge pins which couple the connection systems of the successive links, in order that the links are retained flat on the track of the chain conveyor in the bend zones thereof. Without magnets or other means for keeping the chain links flat, these links tend to come off in the bend zones on the outside of the rails as a result of the pull exerted on the chain, which is naturally undesirable.
Although the bend segment disclosed in EP-A-0.286.173 works very well in practice, a drawback thereof is that it is rather expensive to manufacture. In the design of this bend segment as it is marketed, the magnets are arranged in groups of four in a plastics frame and a bend segment comprises a plurality of these frames arranged in line with each other in a recessed space provided for that purpose in the top surface of the connecting portion between the legs of the U-shaped element, this recessed space continuing partly into the legs of the element. This means that the frames must be inserted one by one into the slot defining the space referred to. Furthermore, because it is unacceptable from the point of view of hygiene that there are gaps between the successive frames and between the frames and the rails, the top of the frames, after these have been arranged, is filled up with a liquid plastics, which, after hardening, is levelled by means of milling. It will be clear that these successive steps prevent an economical and hence inexpensive manufacture of the bend segments.
Further, it has been found in practice that it would be highly desirable if there were a bend segment for a chain conveyor which is suitable both for chains substantially made of plastics and for chains made entirely of steel, since this has the advantage that only one type of bend segment is to be kept in stock and that the user, also after installation of the chain conveyor, can freely choose between the use of steel chains and plastics chains.
The bend segment disclosed in EP-A-0.286.173 is less suitable for steel chains because in certain cases the magnets arranged in that bend segment do not exert sufficient force of attraction on the ends of the ferromagnetic bearing surfaces of the chain links in an outside bend, so that the links still have the tendency to come off the rails in the outside bend. In the known bend segment it is not possible to arrange for the magnets to extend further in lateral direction into the legs of the U-shaped element because this would have an unacceptable adverse effect on the mechanical strength of the bend segment. Nor is it possible to increase the magnetic force by using stronger magnets because in that case the force of attraction becomes too high for plastics chains, thereby causing undue wear. Finally, it is impossible to design the known bend segment to have the standardized height of 27 mm for steel chains.
German Gebrauchsmuster DE-U-89.01563 also describes a bend segment in which the magnets are arranged in the top surface of the connecting portion of a U-shaped plastics element. In fact, with this bend segment, the same problems occur when mounting the magnets as in the bend segment according to EP-A-0.286.173, while further this known bend segment has highly undesirable characteristics from the point of view of hygiene because the middle portion of the bend segment is not sealed in any manner after the magnets have been mounted, so that undesirable gaps are formed. It is true that it is described that the bend segment known from DE-U-89.01563 is suitable for guiding chains having a bearing surface of a magnetizable material, but if this is true at all, the bend segment is mechanically substantially weakened in that the magnets must extend far into the legs on opposite sides and, in view of the magnetic force required, the bend segment is not suitable for guiding substantially plastics chains because the hinge pins thereof would be subject to an excessive force of attraction. Finally, DE-U-89.01563 also shows radial ribs between the rails, but these ribs serve to connect the rails, with completely open spaces present between the ribs. Such a construction is mechanically very weak.
European patent application EP-A-0.159.074 discloses a bend segment that is intended for use with chains made from a ferromagnetic material. This bend segment also comprises a U-shaped plastics element and permanent magnets arranged in chambers formed for that purpose in the bottom of the legs of that element, these chambers extending into the vicinity of the top of the legs. During operation, the permanent magnets arranged in the chambers are pulled up by the material of the chain links against the tops of these chambers, whereby optimum attraction of the chain links is ensured. This known bend segment, however, is entirely unsuited for use with substantially plastics chains.
European patent application EP-A-0.207.577 also describes a bend segment which in fact is also suitable only for use with a chain made of a ferromagnetic material. In this bend segment, which is built up from several loose members and does not consist of a U-shaped element, the magnets are arranged around a bush interconnecting the rails. A magnetic circuit is formed with bushes and plates of a ferromagnetic material, in such a manner that the magnetic force, as in the manner of a horse-shoe type magnet, is concentrated in the top surface of the rails near the ferromagnetic bearing surfaces of the chain links.